Hydraulic pump jack



jam. 2, i940.

J. H. SUTER HYDRAULIC PUMP JACK Filed March 12, 1958 5 Sheets-Sheet l JQHN H. SUTER Jan. 2, 1940. J, H, SUTER HYDRAULIC PUMP JACK Filed March 12, 1938 5 Sheets-Sheet 2 J. H. SUTER HYDRAULIC PUMP JACK mflan 2, 194

Filed March 12, 1938 5 Sheets-Sheet 3 JOHN H. SUTER lNl/ENTOR Jan. 2, 1940.. .1. H. SUTER HYDRAULIC PUMFJAGK Filed March 12, 1958 s Sheets-Sheet 5 I V y/lllllllllllvrllld JOHN H; SUTER lNl E N 70/? 42 Q,

Fla s Patented Jan. 2, I940 TAT f was PATENT OFFICE Application March 12,

3 Claims.

The object of the invention is to provide a light, portable, and inexpensive power'for actuating deep well pumps in oil and water wells.

The apparatus of the invention consists substantially of a power cylinder mounted on and in axial alignment with the well casing; a piston connected with the well pump sucker rods and reciprocating in the cylinder; a source of continuous supply of hydraulic fluid under pres sure, and valve mechanism arranged altemate- 1y .to direct the pressure fluid beneath the piston to produce an upstroke of the pump and to permit the escape of the pressure fluid thus allowing the weight of the rods to produce a downstroke.

This apparatus is capable of various-modifications, principally in the valve mechanism, as follows:

In the first and simplest form, the valve by which the direction of pressure fluid flow is periodically reversed is mechanically or hydraulically actuated in one direction and hydraulical- 1y actuated in the opposite direction, mechanical means being provided for carrying the valve over a possible dead center;

In the second form a valve actuated as above described is utilized as a pilot valve and the main control valve is hydraulically actuated in both directions;

In the third form the main valve is actuated in the same manner as in the second form but additional provisions are made for keeping the hydraulic supply means (ordinarily a pump and motor) operating under a substantially constant full load.

These various forms are illustrated in the attached drawings, in which Fig. 1 is a plan diagram of the first form, for locating subsequent figures;

Fig. 2 is an elevation on the valve side of the apparatus, as on the line 2-2 of Fig. 1;

Fig. 3 is a vertical section through the jack assembly 30, as on the line 3-3 of Fig. 1;

Fig. 4 is a vertical section through the main valve of the jack, as on the line 4-4 of Fig. 1;

Fig. .5 is a similar section through the valve assembly of the second form of the invention;

Fig. 6 is an elevation of the valve side of the apparatus of the third form of the invention;

Fig. '7 is a detail of the valve arrangements of the third form;

Fig. 8 is a detail of a modified form of jack piston, and

Fig. 9 illustrates a device for actuating either the main valve or the pilot valve hydraulically at the endoi the downstroke.

1938, Serial No. 195,452

(Cl. BEL-157) Referring first to Figs. 1 and 2, 20 is a pump adapted to supply a stream of hydraulic fluid under pressure. This may be a gear or vane pump, for example, and may be driven as by an electric motor 2| directly or through a chain or 5 belt 22. A supply of the hydraulic fluid is maintained in a tank 23, which may be closed as shown and provided with a pressure gauge 24 and a release valve 25, or may be open to the atmosphere. 1

The numeral 30 generally indicates this form of the well pump actuating assembly, which for brevity will hereinafter be referred to as the jack. This assembly consists essentially of a working cylinder 3|, a housing 32, a valve chamber 33, 15 and a spacer 34 which screws or is flanged at its lower end to the upper end of the well casing 35, which thus supports the entire assembly.

Referring now to Fig. 3, the working cylinder. 3| is provided with a piston 40 having ring so grooves and split rings 4|. This piston is hollow as indicated at 42, is formed with one or more openings 43 in its lower face, and has a central boss 44 which is bored to .a sliding fit on the polish rod 45. On top of the piston and 25 around the rod is a rod clamp bushing 46 and both the upper face of the piston and the lower face of the bushing are relieved around the rod to receive a packing ring 41. A conventional rod clamp -48 surrounds the rod and rests on the upper end of the bushing. A slip cover 50 of sheet metal surrounding the rod may be used to exclude dust from the upper end of the cylinder.

The lower end of cylinder 3|, which may be a 5 casting or a section of steel tubing, is screwed into housing 32 as at 5|. Below the end of the cylinder the housing is internally enlarged as at 52 to provide an annular channel around the piston when the latter is at its lowermost posi- 40 tion. A thrust pin 53 is brought to a neat sliding fit in a corresponding bore in the housing casting, in such position that its upper and contacts the lower end of the piston as the latter completes its downward travel. The lower end of 45 the pin bears on one end of a rocker arm 54 keyed to a rock shaft 55 which is supported on suitable bearings not shown and, at its forward end, projects through the housing as indicated at 55 in Fig. 2. The opposite end of the rocker arm bears on a cap 56 engaging one end of an open coil spring 31 which is positioned by a rod 58 threaded into the housing at its lower end 59. The tension of this spring is adjusted by a fol- 55 lower 60, termed to a sliding lit in the upper side of the housing, and an adjusting nut 6|. 1

In a medial position in the housing the polish rod 46 passes through a stuiiing box 62 provided with a bolted gland 63. The box is filled with any suitable rod packing, preferably inthe two sections 64 and 65 with a lantern ring 66 interposed, this ring draining through a port 61 into the interior of housing 32.

' The bottom of housing 32 is bolted to or formed integral with a spacermember 68 which is open at its sides to permit access to the stufling boxes.

A flange 69 is bolted to the lower end of thisspacer and carries a stufling box 18 provided with a bolted gland II and suitable packing 12. On the lower face of the .flange is a projection 13- externally threaded as at 14 to screw into a collar 15 or other fitting carried on the end of pump tubing 18.

The spacer member above described'has the advantage of exposing the ends of packing members so that leakage may be detected, and of renderingthe packing glands accessible for adjustment. In many cases, however, it may be dispensed with and stufling box ill utilized for the joint purpose of passing the polish rod out of the cylinder and into the tubing. For example, the lower end of housing member 32 may be flanged and be'bolted to a companion flange on the upper end of the tubing string after the packing 12 is placed and adjusted.

Reierring now to Fig. 4, a valve chamber 83 is formed on or bolted to the face of housing 32 as generally indicated in Fig. 2. This chamber is bored to flt a piston valve 11 and is provided with heads 18 and 19. At one end-the right hand as shown in the figure-a stem is projected from theend of the valve through head 19. The end of this stem engages an adjusting. screw 81 carried in a lever 82 which in turn is keyed to the projecting end of rock shaft 55.

The piston valve 11 is reduced in diameter for a portion or its length as at 83 and the valve chamber body is provided with a port 84 communicating through a channel 85 with the extreme lower end of working cylinder 8l--thls channel 'must not be closed by the piston 48 at any position of the piston. Aport 86 .i'ormed in the valve chamber body affords communication through pipe 61 with storage tank 23 (see Fig. 2); This port is so positioned thatit is wholly closed when 'valve 11 is in the extreme left hand position and is wholly open when the valve is in the extreme right hand position. A similar port 88 affords communication through pipe 89 with the discharge side of hydraulic fluid supply pump 20. This pump draws fluid from tank 28 through pipe 90 (Fig. 2). I

In practice, pipes 85 and 89 may communicate with an annular channel surrounding the valve chamber, in which case ports 84 and 88 as shown in the drawings would be merely the portions of this channel continuous to the ends of these pipes rather than individual openings in the valve chamber wall. The length of the reduced portion 83 of the piston is such that these ports, or the channel, are open in all positions of piston valve 11.

At the extreme left end of the valve chamber bore a port 9| communicates with a pipe 92 which, as shown in Figs. 2 and 3, is connected into working cylinder 3| at various levels as by branches 93-93, each of which is provided with a stop valve or cook 94--94. The uppermost of these branches enters the cylinder below the poor branches may be provided as hereinafter explained.

If desired, though the addition is optional, a

stem 86 may be projected from the left hand end of valve 11 through head 18, the outer end of this stem being yoked to an arm 96 which is pivoted at its lower end in a bracket 91 projected from the housing. To the upper end of this arm is amxed a curved pipe 98 closed at its ends to afford a runway for a heavy metal ball 99. The bracket 91 is so positioned that travel of the piston valve 11 to its extreme right hand position may move the arm clockwise to the same angle to the right of the vertical, or vice versa without the end of pipe 98 striking the housing.

The apparatus above described operates in the following manner. Assuming pump 20 to be in operation and discharging a continuous stream of hydraulic liquid under pressure, and starting with piston 40 at the lower end oi its stroke and valve 11 in the position shown by solid linespressure fluid passes upwardly through port 88, around the reduced portion. 68 of the valve, through port 84 and channel 85 to the lower side of piston 40, lifting it and producing an upstroke oi the polish rod and of the sucker rods and the plunger of the submerged well pump.

One only of the valves 94 will be open, and when the piston in its upward travel uncovers the opening into the cylinder of the branch controlled by this particular valve, 9, small quantity of the hydraulic fluid passes through pipe 92 into the left end of the valve chamber, moving valve 11 to the right hand end of its travel. This movement affords communication between ports 84 and 86 and permits the fluid below piston 40 to be ejected through these ports and pipe 81 by the weight of the sucker rod string which is supported by the polish rod and urges the piston downwardly. At the same time ports 88 and 86 are in communication and the fluid discharged by the pump during the period of the downstroke joins that ejected from the cylinder in returning through pipe 81 to tank 23. It will be seen that the length of the stroke is governed by the valve 94 selected for opening.

When the piston approaches the end of its downstroke its lower end encounters the upper end of pin 53, which is standing in its uppermost position due to the urgency of spring 51. As the piston sinks to the end of its travel, the pin is depressed, lowering the left end of rocker arm 54 and effecting a partial rotation of rock shaft 55. This rotation, in turn, moves the end of the lever 82 toward the left and reverses the position of valve 17, closing discharge port 86 and admitting pressure fluid through pipes 89 and 85 to the lower end of the cylinder, thus beginning an upstroke.

The end of the downstroke is cushioned and destructive impact prevented by the throttling of the ejected hydraulic fluid stream as port 86 is progressively closed by left hand movement of valve 11. As this valve is moved mechanically by the subslding piston, the point of complete cutofi may be adjusted by changing the position of adjusting screw 80 in lever 82. A further cushioning eiTect is produced by a layer of compressed air entrapped within hollow piston 40, which is further compressed, as port 86 is progressively closed, by hydraulic liquid flowing into the piston through openings 43.

The assembly indicated in Fig. 4 at to 99 inelusive is for the purpose of positively completing movement of valve'I'I in either direction. The initial movement of this valve is produced. as said. by hydraulic fluid admitted at the left end of the valve by the uncovering oi one of the ports iii by upward travel of piston 40. As soon as the valve has moved far enough to partly open port 86, the piston begins to move downwardly and almost immediately covers and seals the port 93 through which the valve is being actuated. If, by this time, the valve has not completed its right hand stroke, the pipe 98 will have been carried far enough to the right to cause ball 97 to roll to the right hand end of tube 98, the weight of the ball then causing the mechanical completion of the valve travel. The samecon-v ditions exist at the end of the downstroke.

The hydraulic fluid which actuates the valve in a right hand direction is ejected from the valve chamber when the valve is mechanically moved to the left end of its stroke, but whereas it is taken from below the piston, it is returned through pipe 92 onto the top of the piston, which is at or near the lower end of its travel when the valve reverses. There is thus a small but constant transfer of hydraulic fluid around the piston. To care for this fluid and any additional fluid which may leak past the piston a pipe I connects the upper end of working cylinder 3i with the interior of the housing, which is thus utilized as a sump. A pipe IIII similarly drains into the housing any hydraulic fluid which may leak past valve 11. Finally, a pipe I02 connects the bottom of the housing with the suction side of pump 20 (if the oil level and pressure in tank 23 permit) or to the suction of a small independent pump not shown, by which all liquid draining into the housing is returned to the hydraulic fluid system.

In the modification initially referred to as the second form, the general arrangement of the apparatus is identical with that above described with the exception of means used for moving the hydraulic fluid diversion valve. As the location of the cooperating valve mechanisms on the housing of the jack is a matter of convenience only, they are represented diagrammatically in" Fig. with connections indicated by which they can be tied" into the figures previously described.

Referring tcFig. 5, 33 is the main valve chamber and I03 the pilot valve chamber. The pilot valve chamber is bored to fit the piston valve I01 which is formed with three portions I05, I06, and I01- of reduced diameter. The upper side of the chamber is provided with three ports as shown, ports I08 and I09 communicating with the interiorof housing 32 by means of drilled holes H0 and III. Port II2 communicates through pipe H3 with the source of pressure fluid, as in this instance through pipe 89.

The lowerside of the valve chamber is provided with two ports III and H5 which communicate respectively with the right hand and left hand ends of main valve chamber 33.

The left hand end of pilot valve chamber i03 communicates with pipe 92 which in turn is connected by branches 93-93 with the working cylinder as shown in Figs. 2 and 3. The right hand end of pilot valve I04 has a projecting stem 80 which engages adjusting screw 8i carried by lever 82' as previously described.

In this form the pilot valve instead of the main valve is actuated in a right hand direction by hydraulic fluid transmitted through pipe 92 from beneath piston 40, and in a left hand direcscribed' and as shown in Fla. 8.

The main valve chamber 'isprovided with a piston valve 11 and ports similar to those shown in Fig. 4, to-wit: port 04 communicatingwith the lower end of the working cylinder through pipe 85; port 06 communicatingwith tank 23'through'1 1. The jack piston reaches the lower endof. its stroke, mechanically moving the pilot valve to the left;

2. Pressure fluid enters right end of main valve chamber, moving main valve to the left;

3. Pressure fluid enters jack cylinder-below the piston, producing an upstroke;

4. The jack piston reaches the upper end of its stroke, admitting pressure fluid to the left tion by the engagement of piston 40- with-pin. It at the lower end of the stroke, as above de end of pilot valve chamber and moving pilot valve to the right;

5. Pressure fluid enters left end of main valve" chamber, moving main valve to the right;

6. Pressure fluid escapes from beneath piston, permitting it to make a down stroke and. to return to position I, thus completing the cycle.

It'wlll be understood that the directions given in this and the following descriptiongare illustrative only and refer to the drawings, the directions of movement obviously being reversible by making appropriate changes in the connecting:

channels. 7

To describe the moyements in" detail: the positions in which the two' valves are shown in Fig: 5, steps 1 and 2' have been completed and: pressure fluid from pump 22 is flowing into the cylinder through pipe 89' and channel 05 (port 80 being'closed) thus causing the piston to rise.

It being assumed that one ofthe valvesbk has been opened, the piston continues to rise until.

the corresponding port'in the cylinder wall is I uncovered. Pressure fluidfrom'ibeneaththe. piston then flowsthrough pipe 92flintoxthe left end of the pilot valveJchamber,-* moving pilot valve I04 to the right. This movement places ports hand H5 in .communication,a andr pressure fluidffrom pipe III passes through these ports and pipe; IIG- into the'left end ofj'main valve:

ton escapes (under the urgency of the weight or the rod string) through channel and" ports 84 and 86 into pipe 81, through whichit returns i to the suction side of the pressure pump. At the.

same time ports 88 and 86 are incommunication I through annulus 83 and the delivery of the pressure pump is thus bypassed back to the suction v side through pipe 81.

When the piston reaches the lower end'of its stroke, it encounters pin 53 (Fig; 3) and'through arms 54 and 82 moves pilot valve IM to the left.

Pressure fluid from pipe I I3 then passes throughports H2 and land pipe II'I into the right end of main valve chamber, moving the main valve to the left and ejecting the fluid from the left end of the main valve chamber through pipe H8 and pilot valve ports H5, I09, and Ill into housing 32. With the main valve in the left hand position, port 86 is closed and pressure fluid from pipe 39 passes through ports 88 and 84 and channel 85 into the cylinder beneath the piston, thus initiatinga second upstroke and completing the cycle of movements.

In the use of either of the above forms, a portion of the dead weight of the rod string may be counterbalanced by carrying a suitable pneumatic pressure on the hydraulic fluid column in tank 23. Thus, for example, if it is found that a hydraulic fluid pressure of .300 pounds per square inch is required to raise the piston and its load at the maximum speed required and that the Weight of the load is sufficient to return the piston against a back pressure of 250 pounds, the latter pressure may be maintained on the air above the oil. column in tank 23 by constantly supplying a minute quantity of air to the tank and setting relief valve 25 at the pneumatic pressure required. This air may well be supplied by an auxiliary pump used to return drainings from housing 32 to the pressure side of the system by so adjusting its capacity as to cause it to take in a little air along with the drainage liquid.

The forms above described use the hydraulic fluid under a-fiuctuating pressure which rises to a peak depending on the load during the pumping stroke and drops to the back pressure (if any) in'tank' 23, plus frictional resistance of return pipes and ports, during the return stroke. Thus the pump does useful work only during the pumping stroke (th'eupstroke of the jack piston) while during the return stroke the hydraulic fluid is bypassed without doing any work. Thus during more or less half the period of the stroke cycle the hydraulic pressure pump is idling against the considerable back pressure required to prevent unduly rapid drop of the rod string. In the third form of the invention this waste of power is avoided and a smaller pump and motor made available by directing a substantially constant hydraulic stream of reduced volume into a storage vessel maintained under a slightly fluctuating pneumatic pressure sufficient at-its lowest point to raise the jack piston with its load, and admitting fluid to the jack cylinder from this vessel instead of directly from the pump.

This arrangement, which functions in the general manner above described but with the use of. two storage tanks and a somewhat different valve arrangement, avoids any bypassing of hydraulic fluid while permitting the pump to run constantly.

Referring to Figs. 6 and 7, the third form has a pump driven by a motor 2!, a high pressure fluid supply tank I20 and a low pressure fluid supply tank 23. The pump discharges only into tank'l20, through pipe 89, and takes suction only on tank 23, through pipe 90.

The main valve chamber I2I is provided with a piston valve I22 having two reduced portions I23 and I24 The pilot valve chamber I25 is provided with a piston valve I26 having three reduced portions I21, I28, and I29, The right hand end of piston I26 projects as at I30 and is engaged by the end of lever 82 to be mechanically moved toward the left as above described in connction with the first form of the apparatus. The left hand end of the pilot valve chamber communicates through pipe 92 with any one of a series of ports formed in the side of working cylinder 3|, also as previously described.

With the pilot valve in the position shown and the piston at the end of the down stroke, pressure fluid from high pressure tank I 20 passes through pipe I30, ports I3I and I32, and pipe I33 into the left end of main valve chamber I 2 I, thus moving main valve I22 to the right hand end of its stroke. This movement places ports I34 and I35 in communication, simultaneously closing port I36, and high pressure fluid flows from tank I20 through pipes I31 and I38 into the lower end of working cylinder 3|, raising the piston. The fluid displaced from the right end of the main valve chamber by this right hand movement passes through pipe I39, ports I40 and MI, and pipe I42 into low pressure tank 23 or into housing 32.

When the piston 40 has been lifted to such height as to uncover one of the ports 94, pressure fluid flows through pipe 92 into the left end of pilot valve chamber I25, moving pilot valve I26 to the right hand end of its stroke. This movement places ports I 3I and I40 in communication and pressure fluid from tank I20 flows through pipe I30, Ports I3I and I40, and pipe I39 into the right end of main valve chamber I2I, moving main valve I22 to the left end of its travel. In this position communication between ports I35 and I34 is interrupted and pressure fluid passes from the lower end of the working cylinder 3| through pipe I38, ports I35 and I36, and pipe I43 into low pressure tank 23. The fluid displaced in this left hand movement of the main valve passes through pipe I33, ports I32 and I44, and pipe I45 into tank 23 or into housing 32.

A suitable means for maintaining a pneumatic cushion above the oil level in tank I20 is shown in Fig. 6. This arrangement consists of any suitable small pump I10 taking suction from the bottom of housing 32 as through pipe I02. This pump discharges into the upper part of tank I20 through pipe "I, thus returning to the circulating supply of hydraulic fluid the liquid collecting in the housing as previously described. The speed of this pump should be so adjusted that in addition to removing liquid from the bottom of the housing as fast as it collects, a small continuous supply of air will also be drawn into the suction of the pump and discharged into tank I23. This air passes out of tank I20 through pipe I12 in which is interposed a relief valve or pressure regulator I13 set at the working pressure which it is necessary to maintain in this tank. From this regulator the air passes through pipe I14 to a second regulator I15 adjusted to relieve at a pressure lower than that fixed by regulator I13. A pipe I16 is branched from pipe I14 into the top of tank 23 and thus the pressure in this tank is governed by the adjustment of regulator I15. The air lifted by pump I10 is thus finally discharged from the system through pipe I11. Regulator I15 may be adjusted to maintain a superatmospheric pressure in tank 23 to partially counterbalance the load on the jack or, if preferred, it may be backed off in order to maintain tank 23 at atmospheric pressure.

A modified form of piston arrangement which has advantages over that shown in Fig. 3 is illustrated in Fig. 8. In this form the piston 40 is provided with a riser I surrounding the polish rod and split at its upper end I5I to be clamped to the polish rod in the usual manner. This riser is flanged at its lower end and bolted to the piston head as at I52. A cap ring I53 is screwed or otherwise attached to the upper end of jack cylinder 3| and is projected inwardly to form a shoulder I54 to engage the upper end of the piston while allowing clamp I6I to pass through. The overflow opening I55 into pipe IIlIl is so located that clamp I5I will project above ring I53 when this opening is partly uncovered by upward movement of the piston. To insure against upward slippage of the piston on the polish rod it is often desirable to place an independent rod clamp I56 above clamp I5I.

One advantage of this arrangement is that the piston may be raised by hydraulic fluid pressure until the opening of port I55 stops its further movement, after which the polish rod may be raised or lowered as regards the piston by loosening clamps I5I and I56. Another advantage is that by disconnecting the polish rod below the jack assembly and the assembly from the tubing head and the pipes through which hydraulic fluid is conveyed, the entire jack assembly may be swung up in the derrick from the upper end of the polish rod by raising the rod until the upper end of piston 40 engages shoulder I54.

For the left hand movement of either the main valve of the first form or the pilot valve of the second or third, it is possible to substitute for the mechanical linkage indicated by numerals 53 to 6|] and BI-82 of Figs. 3, 4, 5, and 7 a means for actuating the valve hydraulically in response to the downward movement of the piston at the end of the stroke.

In Fig. 9, 3| is a. fragment of the lower end of the jack cylinder, 32 the housing member, and 40 the piston shown in preceding figures. A tappet valve I60 is passed into the lower end of the cylinder through the upper wall of the housing and is supported in position by a spring I6I of such stillness as to prevent the valve from being forced downwardly by the maximum fluid pressure existin in the cylinder. The body of the housing surrounding the tappet valve is provided with three channels, I62 leading from the interior of the cylinder to the bore I63 in which the tappet valve slides, I64 leadingirom the bore to the interior of housing 32, I65 leading to the right hand end oi main valve chamber 33 (Fig. 4) or pilot valve chamber I03 (Fig. 5) or I25 (Fig. 7) as the case may be.

The tappet valve has two grooves I66 and I6! so arranged that when piston 40, in its downward movement, has depressed the tappet valve to the end of its travel, channel I64 is closed and channel I62 is placed in communication with channel I65 through groove I66, thus permitting hydraulic fluid to pass into the right end of the main or pilot valve chamber and move the valve to the left hand. As the piston then rises and the spring returns the tappet valve to the position shown in Fig. 9, channel I62 is closed and channel I65 is placed in communication with channel I64 through groove I61, thus permitting the fluid ejected from the main or pilot valve chamber by right hand movement of the valve to pass into housing 32 from which it is removed as previously described.

I claim as my invention:

1. In a hydraulic pump jack having a cylinder and a piston vertically reciprocating therein: a main valve arranged alternately to admit hydraulic fluid to and release said fluid from the lower end of said cylinder; a pilot valve ar-- ranged to reciprocate said main valve by admitting hydraulic fiuid alternately to its opposite ends; mechanical means actuated by contact with said piston for moving said pilot valve to one end of its travel at the end of the downstroke, and hydraulic means actuated by pressure transmitted from within said cylinder for moving said pilot valve to the opposite end of its travel at the end of the upstroke.

2. In a hydraulic pump jack having a cylinder and a piston vertically reciprocating therein: a main valve arranged alternately to admit hydraulic fluid to and release said fluid from the lower end of said cylinder; a secondary valve actuated by contact with said piston to transmit fluid from the lower end of said cylinder to said main valve and thereby to move said main valve hydraulically to the fluid admitting position at the end of the downstroke, and means for transmitting hydraulic'fluid from the upper part of said cylinder to said main valve and thereby to actuate said main valve to the fluid releasing position at the end of the upstroke.

3. In a hydraulic pump jack having a cylinder and a piston vertically reciprocating therein: a main valve arranged alternately to admit hydraulic fluid to and release said fluid from the lower end of said cylinder; a pilot valve arranged to reciprocate said main valve by admitting hydraulic fluid alternately to its opposite ends; a secondary valve actuated by contact with said piston and controlling a channel for transmitting hydraulic fluid from said cylinder to said pilot valve and thereby moving said pilot valve hydraulically to one end of its travel at the end of the downstroke, and means for transmitting hydraulic pressure to said pilot valve from the upper part of said cylinder for moving said pilot valve to the opposite end of its travel at the end of the upstroke.

JOHN H. SUTER. 

